An internal combustion engine of the stated type is used as a motor vehicle drive unit. Within the context of the present disclosure, the expression “internal combustion engine” encompasses diesel engines and Otto-cycle engines and also hybrid internal combustion engines, which utilize a hybrid combustion process, and hybrid drives which comprise not only the internal combustion engine but also an electric machine which can be connected in terms of drive to the internal combustion engine and which receives power from the internal combustion engine or which, as a switchable auxiliary drive, additionally outputs power.
In the development of internal combustion engines, it is sought to minimize fuel consumption. Furthermore, a reduction of the pollutant emissions is sought in order to be able to comply with future limit values for pollutant emissions.
Internal combustion engines are ever more commonly being equipped with supercharging, wherein supercharging may be a method for increasing power, in which the charge air used for the combustion process in the engine is compressed, as a result of which a greater mass of charge air can be supplied to each cylinder per working cycle. In this way, the fuel mass and therefore the mean pressure can be increased.
Supercharging is a suitable means for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In any case, supercharging leads to an increase in volumetric power output and a more expedient power-to-weight ratio. If the swept volume is reduced, it is possible, given the same vehicle boundary conditions, to shift the load collective toward higher loads, at which the specific fuel consumption is lower. Supercharging of an internal combustion engine consequently assists in the efforts to minimize fuel consumption, that is to say to improve the efficiency of the internal combustion engine.
By means of a suitable transmission configuration, it is additionally possible to realize so-called downspeeding, whereby a lower specific fuel consumption is likewise achieved. In the case of downspeeding, use is made of the fact that the specific fuel consumption at low engine speeds is generally lower, in particular in the presence of relatively high loads.
With targeted configuration of the supercharging, it is also possible to obtain decreased exhaust-gas emissions. With suitable supercharging for example of a diesel engine, the nitrogen oxide emissions can therefore be reduced without any losses in efficiency. At the same time, the hydrocarbon emissions can be positively influenced. The emissions of carbon dioxide, which correlate directly with fuel consumption, likewise decrease with falling fuel consumption.
To adhere to future limit values for pollutant emissions, however, further measures are desired. Here, the focus of the development work is on inter alia the reduction of nitrogen oxide emissions, which are of high relevance in particular in diesel engines. Since the formation of nitrogen oxides occurs not only an excess of air but also high temperatures, one concept for lowering the nitrogen oxide emissions consists in using combustion processes with lower combustion temperatures.
Here, exhaust-gas recirculation (EGR), that is to say the recirculation of combustion gases from the outlet side to the inlet side of an engine, is expedient in achieving this aim, wherein it is possible for the nitrogen oxide emissions to be considerably reduced with increasing EGR rate. Here, the EGR rate xEGR is determined as xEGR=mEGR/(mEGR+mfresh air), where mEGR denotes the mass of recirculated exhaust gas and mfresh air denotes the supplied fresh air. The oxygen provided via exhaust-gas recirculation may possibly be taken into consideration.
To obtain a considerable reduction in nitrogen oxide emissions, high EGR rates may be desired, which may be of the order of magnitude of xEGR≈60% to 70% or more. Such high recirculation rates may demand cooling of the EGR, by which means the temperature of the exhaust gas is reduced and the density of the exhaust gas increased, so that a greater mass of exhaust gas can be recirculated. Consequently, an exhaust-gas recirculation arrangement is commonly equipped with a cooler. The exhaust-gas recirculation arrangement of the internal combustion engine to which the present disclosure relates also has a cooling arrangement, that is to say at least one EGR cooler, which has a coolant-conducting coolant jacket which serves for the transfer of heat between exhaust gas and coolant.
Problems can arise during the introduction of the recirculated exhaust gas into the intake system if the temperature of the recirculated hot exhaust gas decreases and condensate forms.
Firstly, condensate can form if the recirculated hot exhaust gas meets, and is mixed with, cool fresh air in the intake system. The EGR gas cools down, whereas the temperature of the fresh air is increased. The temperature of the mixture of fresh air and EGR, that is to say the temperature of the combustion air, lies below the temperature of the EGR. During the course of the cooling of the exhaust gas, liquids previously contained in the EGR and/or in the combustion air still in gaseous form, in particular water, may condense if the dew point temperature of a component of the gaseous combustion-air flow is undershot. Condensate formation occurs in the free combustion-air flow, wherein contaminants in the combustion air often form the starting point for the formation of condensate droplets.
Secondly, condensate can form when the EGR and/or the combustion air impinges on the internal wall of the intake system, as the wall temperature generally lies below the dew point temperature of the relevant gaseous components.
Condensate and condensate droplets are undesirable and may to increased noise emissions in the intake system and possibly to degradation of the impeller blades of a compressor impeller, which is arranged in the intake system, of a supercharger or of an exhaust-gas turbocharger. The latter effect is associated with a reduction in efficiency of the compressor.
With regard to the problem of the above-described condensate formation, too, an EGR cooler may be expedient or helpful. The cooling of the exhaust gas for recirculation during the course of the recirculation has the effect that the condensate does not form for the first time in the intake system but forms already during the recirculation, and can be separated off during the course of the recirculation.
A disadvantage of the EGR coolers according to previous attempts is that the useful exhaust-gas energy, that is to say the heat that can be extracted from the exhaust gas in the cooler by means of coolant, is out of principle only available and usable when exhaust gas is being recirculated. According to the previous examples, if the exhaust-gas recirculation arrangement has been deactivated, such that no exhaust gas is being recirculated, the exhaust-gas energy of the hot exhaust gas may be wasted. If it were possible to utilize said exhaust-gas energy, that is to say to recover said exhaust-gas energy in the context of energy recovery, it would be possible to achieve further efficiency advantages in the internal combustion engine.
The energy of the hot exhaust gas could for example be utilized to reduce the friction losses and thus the fuel consumption of the internal combustion engine. Here, rapid warming of the engine oil by means of exhaust-gas heat, in particular after a cold start, could be expedient. Fast warming of the engine oil during the warm-up phase of the internal combustion engine ensures a correspondingly fast decrease in the viscosity of the oil and thus a reduction in friction and friction losses, in particular in the bearings which are supplied with oil, for example the bearings of the crankshaft.
Here, the oil could for example be actively warmed by means of a heating device. For this purpose, it is possible in the warm-up phase for a coolant-operated oil cooler to be utilized, contrary to its intended purpose, for cooling the oil.
Fast warming of the engine oil in order to reduce friction losses may basically also be aided by means of fast heating of the internal combustion engine itself, which in turn is assisted, that is to say forced, by virtue of as little heat as possible being extracted from the internal combustion engine during the warm-up phase.
In this respect, in the case of a liquid-cooled internal combustion engine, it may also be expedient for heat to be supplied to the coolant of the engine cooling arrangement, in particular in the warm-up phase or after a cold start. It would be possible for the exhaust-gas energy to be utilized for warming the coolant of the engine cooling arrangement.
It is also a disadvantage of EGR coolers according to the previous attempts that the coolers may not be configured to perform energy recovery, with the focus rather being on the cooling of the exhaust gas, that is to say the pure cooling effect. Here, the cooler may be able to cope with all exhaust-gas flow rates for recirculation via the exhaust-gas recirculation arrangement during the operation of the internal combustion engine. In particular, the maximum exhaust-gas flow rate for recirculation and for cooling may be allowed for. The range of variation of the exhaust-gas flow rate for recirculation via the exhaust-gas recirculation arrangement leads to widely varying pressure conditions at the cooler. The pressure gradient across the cooler changes noticeably in a manner dependent on the exhaust-gas flow rate for recirculation, that is to say in such a relevant manner that it may be taken into consideration in the control or setting of the recirculation rate. The resulting interaction leads to certain dynamics, and necessitates correspondingly complex or intricate control of the exhaust-gas recirculation arrangement.
In one example, the issues described above may be addressed by a supercharged internal combustion engine having at least one cylinder, an intake system for supplying air to the at least one cylinder, an exhaust-gas discharge system for discharging the exhaust gases, and an exhaust-gas recirculation arrangement which comprises at least one recirculation line, with at least one cooler and at least one control element being provided in the at least one recirculation line for the purposes of setting a predefinable exhaust-gas flow rate for recirculation, the internal combustion engine further comprising at least two recirculation lines, in which there is arranged in each case one cooler, the coolers being arranged in parallel and being usable independently of one another for cooling exhaust gas for the purposes of energy recovery.
In the case of the internal combustion engine according to the disclosure, multiple coolers are provided by means of which exhaust gas for recirculation can be cooled. In some cases, the coolers can be activated, and used for the cooling of exhaust gas for recirculation, simultaneously. In this way, the cooling power of the EGR cooling arrangement, or the number of EGR coolers, can be adapted to the exhaust-gas flow rate for cooling. The benefits of which will be described in greater detail below.
The pressure gradient across a single cooler changes during the operation of the cooler to a lesser extent than in the previous examples, because the exhaust-gas flow rates to be cooled or coped with by said cooler vary to a lesser extent.
In the case of relatively low recirculation rates, it is possible according to the disclosure for one cooler to be used for cooling the exhaust gas for recirculation. If the exhaust-gas flow rate for recirculation and for cooling then increases, it is possible, for example in the event of an exceedance of a predefinable exhaust-gas flow rate, for a further cooler to be activated in order to cool exhaust gas and contribute to the cooling of the exhaust gas for recirculation. Depending on the number of EGR coolers provided, if for example three, four or more coolers are provided, activation can be performed several times or in succession. The control or adjustment of the recirculation rate reacts less dynamically.
Furthermore, the line system of the exhaust-gas-conducting lines may be configured or switchable in such a way that, even when the exhaust-gas recirculation arrangement has been deactivated, when no exhaust gas is being recirculated, one cooler is utilized and used for cooling exhaust gas, such that, by contrast to the previous examples, the energy inherent in the exhaust gas can be utilized, or made utilizable, in the context of energy recovery even when the exhaust-gas recirculation arrangement has been deactivated.
The exhaust-gas energy can be utilized for example in the warm-up phase or after a cold start for warming the engine oil of the internal combustion engine and thus reducing the friction losses of the internal combustion engine. In the case of a liquid-cooled internal combustion engine, the exhaust-gas energy can be utilized for warming the coolant of the engine cooling arrangement and thus accelerating the heating of the internal combustion engine. Both measures improve or increase the efficiency of the internal combustion engine.
The EGR coolers of the internal combustion engine according to the disclosure are configured both with regard to effective cooling and with regard to the energy recovery, that is to say the utilization of the exhaust-gas energy. According to the disclosure, both aspects are provided.
The internal combustion engine to which the present disclosure relates is a supercharged internal combustion engine. Reference is made to the benefits already mentioned, and the statements made, in conjunction with supercharging.
The internal combustion engine according to the disclosure thus may be a supercharged internal combustion engine where the exhaust-gas energy can be utilized more effectively than in the previous examples, and which is further improved with regard to the exhaust-gas recirculation.
According to the disclosure, the at least two recirculation lines belong to one exhaust-gas recirculation arrangement, that is to say to a single, or the same, exhaust-gas recirculation arrangement. An internal combustion engine which is equipped with a low-pressure EGR arrangement comprising a recirculation line and with a high-pressure EGR arrangement comprising a recirculation line has two recirculation lines, but not an exhaust-gas recirculation arrangement according to the disclosure.
Embodiments of the internal combustion engine are desired in which the coolers form an integral structural unit. A prefabricated assembly which comprises the coolers and which constitutes the entire cooling unit simplifies the installation of the exhaust-gas recirculation arrangement and of the internal combustion engine as a whole, and thus also reduces costs.
Embodiments of the internal combustion engine may also be desired in which the coolers are in the form of individual, separate coolers. In accordance with a modular principle, it is then possible using individual coolers to form different exhaust-gas recirculation arrangements or to equip different internal combustion engines.
Further alternative embodiments of the internal combustion engine according to the disclosure will be discussed herein.
Embodiments of the supercharged internal combustion engine may be desired may include one or more of a first recirculation line provided in which a first cooler is arranged and which, using at least one control element, is at least connectable upstream of the first cooler to the exhaust-gas discharge system and downstream of the first cooler to the intake system, a second recirculation line provided in which a second cooler is arranged and which, using at least one control element, is at least connectable upstream of the second cooler to the exhaust-gas discharge system and downstream of the second cooler selectively to the intake system or to the exhaust-gas discharge system, and each cooler has, for the purposes of energy recovery, at least one coolant-conducting coolant jacket which serves for the transfer of heat between the exhaust gas and the coolant.
It may be desired that no exhaust gas is recirculated after a cold start of the internal combustion engine, because, upon the introduction of the recirculated exhaust gas into the still-cold intake system, a particularly large amount of condensate may form. With the then deactivated exhaust-gas recirculation arrangement, it is the case in the previous examples that the exhaust-gas energy of the hot exhaust gas cannot be utilized, despite the fact that a demand for warming the engine oil and the internal combustion engine in targeted fashion exists specifically after a cold start of the internal combustion engine.
By contrast to this, in the case of the present embodiment, the exhaust-gas energy of the hot exhaust gas can be utilized even when the exhaust-gas recirculation arrangement has been deactivated; at least by means of the second cooler which is selectively connectable, downstream, to the intake system or to the exhaust-gas discharge system, with at least one control element serving for this purpose by means of which the exhaust-gas-conducting lines can be correspondingly switched, specifically connected to the exhaust-gas discharge system. It is thus possible even when the exhaust-gas recirculation arrangement has been deactivated for heat to be transferred from the exhaust gas to the coolant of the second cooler, wherein the coolant flowing or circulating through the second cooler discharges the heat from the interior of the second cooler and supplies it for a predefinable use, whereby the efficiency of the internal combustion engine is increased.
Embodiments of the supercharged internal combustion engine may include in which the first recirculation line is, downstream of the first cooler, at least connectable selectively to the intake system or to the exhaust-gas discharge system using at least one control element.
In the above embodiment, when the exhaust-gas recirculation arrangement has been deactivated, the exhaust-gas energy of the hot exhaust gas can be also be utilized by means of the first cooler, which in the present case is likewise selectively connectable, downstream, to the intake system or to the exhaust-gas discharge system, with at least one control element serving for this purpose by means of which the exhaust-gas-conducting lines can be correspondingly switched, specifically connected to the exhaust-gas discharge system.
Thus, when the exhaust-gas recirculation arrangement has been deactivated, it is possible for both coolers of the exhaust-gas recirculation arrangement to be utilized for energy recovery and for improving the efficiency of the internal combustion engine.
It is also possible for the first and/or second cooler to be permanently connected, upstream, to the exhaust-gas discharge system, wherein at least one control element provided downstream of the cooler is adjusted or switched such that the cooler is connected, downstream, to the intake system or to the exhaust-gas discharge system.
Embodiments of the supercharged internal combustion engine may further include in which the first recirculation line branches off from the exhaust-gas discharge system so as to form a first junction point and opens into the intake system so as to form a second junction point.
In this context, embodiments of the supercharged internal combustion engine may further include in which a first control element is provided in the first recirculation line at the second junction point.
The first control element functions as an EGR valve and, when the exhaust-gas recirculation arrangement is active, serves for the adjustment of the recirculation rate, or at least of the exhaust-gas flow rate recirculated via the first recirculation line. The use of a combination valve arranged at the second junction point permits dimensioning of the recirculated exhaust-gas flow rate and at the same time throttling of the intake fresh-air flow rate.
A combination valve of said type may for example be a flap which is pivotable about an axis running transversely with respect to the fresh-air flow, in such a way that, in a first end position, the front side of the flap blocks the intake system, and at the same time the recirculation line is opened up, and, in a second end position, the back side of the flap covers the recirculation line, and at the same time the intake system is opened up. An additional valve body which is connected and thereby mechanically coupled to the flap either opens up or blocks the recirculation line. Whereas the flap serves for the adjustment of the air flow rate supplied via the intake system, the valve body effects the metering of the recirculated exhaust-gas flow rate.
Embodiments of the supercharged internal combustion engine may further include in which the second recirculation line branches off from the exhaust-gas discharge system so as to form a third junction point and opens into the intake system so as to form a fourth junction point.
However, in the above-described context, in particular, embodiments of the supercharged internal combustion engine may further include in which the second recirculation line branches off from the exhaust-gas discharge system so as to form a third junction point and opens into the first recirculation line downstream of the first cooler so as to form a fourth junction point.
Then, when the exhaust-gas recirculation arrangement is active, a control element provided at the second junction point can serve for adjusting the entire recirculation rate, specifically both the exhaust-gas flow rate recirculated by the first recirculation line and the exhaust-gas flow rate recirculated by the second recirculation line.
Here, embodiments of the supercharged internal combustion engine may further include in which a second control element is provided in the second recirculation line downstream of the second cooler. Said second control element may be used for activating and deactivating the second cooler.
The second control element may however in some cases also be utilized for connecting the second cooler, downstream, to the exhaust-gas discharge system, for which purpose further exhaust-gas-conducting lines may be provided if desired. The second cooler then does not cool any exhaust gas for recirculation. Rather, the second cooler cools exhaust gas which has been extracted from the exhaust-gas discharge system and which is introduced into the exhaust-gas discharge system again. That is to say, in the present case, the second cooler serves only for energy recovery, that is to say for making the energy inherent in the exhaust gas utilizable.
For the reasons stated above, embodiments of the supercharged internal combustion engine may further include in which an exhaust-gas-conducting line is provided which branches off from the second recirculation line downstream of the second cooler so as to form a fifth junction point and opens into the exhaust-gas discharge system so as to form a sixth junction point.
Here, embodiments of the supercharged internal combustion engine may further include in which the second control element is arranged at the fifth junction point.
In embodiments in which the second recirculation line opens into the first recirculation line downstream of the first cooler so as to form a fourth junction point, it is then also possible for the first cooler to be connected, downstream, to the exhaust-gas discharge system via the further exhaust-gas-conducting line. Then, the first cooler does not cool any exhaust gas for recirculation, but rather cools exhaust gas that is introduced into the exhaust-gas discharge system again. Then, both coolers serve for energy recovery when the exhaust-gas recirculation arrangement has been deactivated.
In embodiments in which an exhaust-gas-conducting line branches off from the second recirculation line downstream of the second cooler and opens into the exhaust-gas discharge system so as to form a sixth junction point, it may be desired for the sixth junction point to be arranged in the exhaust-gas discharge system downstream of the first and third junction points.
In this context, embodiments of the supercharged internal combustion engine may further include in which a throttle element is arranged in the exhaust-gas discharge system upstream of the sixth junction point and downstream of the first and third junction points. The throttle element serves for increasing the exhaust-gas pressure upstream in the exhaust-gas discharge system, whereby the driving pressure gradients across the cooler are likewise increased and a path for the exhaust gas to circumvent the cooler is eliminated, or the bypassing of the cooler is impeded.
To generate the desired pressure gradient, it is additionally possible for a shut-off element to be provided upstream of the point at which the exhaust-gas recirculation arrangement opens into the intake system, in order, at the inlet side, to reduce the pressure upstream of the compressor.
Embodiments of the supercharged internal combustion engine may further include in which at least one compressor which can be driven by means of an auxiliary drive is arranged in the intake system.
A compressor that can be driven by means of an auxiliary drive, that is to say a supercharger, in relation to an exhaust-gas turbocharger consists in that the supercharger can generate, and may make available, the demanded charge pressure through a plurality of conditions, specifically regardless of the operating state of the internal combustion engine. This applies in particular to a supercharger which can be driven electrically by means of an electric machine, and is therefore independent of the rotational speed of the crankshaft.
In the previous examples, it is specifically the case that difficulties are encountered in achieving an increase in power in all engine speed ranges by means of exhaust-gas turbocharging. A relatively severe torque drop is observed in the event of a certain engine speed being undershot. Said torque drop is understandable if one takes into consideration that the charge pressure ratio is dependent on the turbine pressure ratio or the turbine power. If the engine speed is reduced, this leads to a smaller exhaust-gas mass flow and therefore to a lower turbine pressure ratio or a lower turbine power. Consequently, toward lower engine speeds, the charge pressure ratio likewise decreases. This equates to a torque drop.
Embodiments of the supercharged internal combustion engine may nevertheless may further include in which at least one exhaust-gas turbocharger is provided, which comprises a turbine arranged in the exhaust-gas discharge system and a compressor arranged in the intake system. In an exhaust-gas turbocharger, a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow is fed to the turbine and expands in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy supplied by the exhaust-gas flow to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor conveys and compresses the charge air fed to it, as a result of which supercharging of the cylinders is obtained. A charge-air cooler is advantageously provided in the intake system downstream of the compressor, by means of which charge-air cooler the compressed charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thereby increases the density of the charge air, such that the cooler also contributes to improved charging of the cylinders, that is to say to a greater air mass. In effect, compression by cooling is obtained.
An exhaust-gas turbocharger in relation to a supercharger—which can be driven by means of an auxiliary drive—consists in that an exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases, whereas a supercharger draws the energy needed for driving it directly or indirectly from the internal combustion engine and thus adversely affects, that is to say reduces, the efficiency, at least for as long as the drive energy does not originate from an energy recovery source.
If the supercharger is not one that can be driven by means of an electric machine, that is to say electrically, a mechanical or kinematic connection for power transmission is generally needed between the supercharger and the internal combustion engine, which also adversely affects or determines the packaging in the engine bay.
To be able to counteract a torque drop at low engine speeds, embodiments of the internal combustion engine are particularly advantageous in which at least two exhaust-gas turbochargers are provided. Specifically, if the engine speed is reduced, this leads to a smaller exhaust-gas mass flow and therefore to a lower charge-pressure ratio.
Through the use of multiple exhaust-gas turbochargers, for example multiple exhaust-gas turbochargers connected in series or parallel, the torque characteristic of a supercharged internal combustion engine can be noticeably improved.
In order to improve the torque characteristic, it is possible, in addition to the at least one exhaust-gas turbocharger, for a further compressor to also be provided, specifically either a supercharger that can be driven by means of an auxiliary drive or a compressor of a further exhaust-gas turbocharger.
In this context, embodiments of the supercharged internal combustion engine may further include in which the recirculation lines open into the intake system downstream of the compressor.
In the case of a so-called high-pressure EGR arrangement, the exhaust gas is introduced into the intake system downstream of the compressor. Here, to provide or ensure the pressure gradient, needed for a recirculation, between the exhaust-gas discharge system and the intake system, in the case of an exhaust-gas turbocharging arrangement the exhaust gas is preferably, and commonly, extracted from the exhaust-gas discharge system upstream of the associated turbine. High-pressure EGR may not pass the compressor, and therefore does not have to be subjected to exhaust-gas aftertreatment, for example in a particle filter, before the recirculation. There is no risk of deposits in the compressor which change the geometry of the compressor, in particular the flow cross sections, and thereby impair the efficiency of the compressor. Condensate formation occurs—if at all—downstream of the compressor, which also, during the course of the compression, heats the charge air that is supplied to it, and thereby prevents or counteracts condensate formation.
Embodiments of the supercharged internal combustion engine may further include in which the recirculation lines open into the intake system upstream of the compressor.
During the operation of an internal combustion engine with exhaust-gas turbocharging and the simultaneous use of a high-pressure EGR arrangement, a conflict may arise when the recirculated exhaust gas is extracted from the exhaust-gas discharge system upstream of the turbine and is no longer available for driving the turbine.
In the event of an increase in the exhaust-gas recirculation rate, the exhaust-gas flow introduced into the turbine simultaneously decreases. The reduced exhaust-gas mass flow through the turbine leads to a lower turbine pressure ratio, as a result of which the charge pressure ratio also falls, which equates to a smaller compressor mass flow. Aside from the decreasing charge pressure, problems may additionally arise in the operation of the compressor with regard to the surge limit. Pollutant emissions may increase, for example with regard to the formation of soot during an acceleration in the case of diesel engines.
For this reason, adequately high charge pressures with simultaneously high exhaust-gas recirculation rates are desired. One approach to a solution is so-called low-pressure EGR, by means of which exhaust gas that has already flowed through the turbine is recirculated into the intake system. For this purpose, the low-pressure EGR arrangement extracts exhaust gas from the exhaust-gas discharge system downstream of the turbine and conducts said exhaust gas into the intake system preferably upstream of the compressor, in order to be able to realize the pressure gradient, desired for a recirculation, between the exhaust-gas discharge system and the intake system.
The exhaust gas which is recirculated via the low-pressure EGR arrangement is mixed with fresh air upstream of the compressor. The mixture of fresh air and recirculated exhaust gas produced in this way forms the charge air which is supplied to the compressor and compressed, wherein the compressed charge air is cooled, downstream of the compressor, in a charge-air cooler.
Since exhaust gas is conducted through the compressor, the exhaust gas is preferably subjected to exhaust-gas aftertreatment downstream of the turbine. The low-pressure EGR arrangement may also be combined with a high-pressure EGR arrangement. In one example, the exhaust-gas aftertreatment may include a particulate filter so that particulates in the low-pressure EGR do not impinge onto surfaces of the compressor.
For the reasons already stated, embodiments of the supercharged internal combustion engine may further include in which the recirculation lines branch off from the exhaust-gas discharge system upstream of the turbine.
Embodiments of the supercharged internal combustion engine may further include in which the turbine of an exhaust-gas turbocharger that is provided has a variable turbine geometry, which permits an extensive adaptation to the operation of the internal combustion engine through adjustment of the turbine geometry or of the effective turbine cross section. Here, adjustable guide blades for influencing the flow direction are arranged in the inlet region of the turbine. By contrast to the impeller blades of the rotating impeller, the guide blades do not rotate with the shaft of the turbine.
If the turbine has a fixed, invariable geometry, the guide blades are arranged in the inlet region so as to be not only stationary but rather also completely immovable, that is to say rigidly fixed, if a guide device is provided at all. By contrast, in the case of a variable geometry, the guide blades are duly arranged so as to be stationary but not so as to be completely immovable, rather so as to be rotatable about their axis, such that the flow approaching the impeller blades can be influenced.
Through adjustment of the turbine geometry, it is possible for the exhaust-gas pressure upstream of the turbine to be influenced, and thus for the pressure gradient between the exhaust-gas discharge system and intake system, and thus the recirculation rate of the high-pressure EGR arrangement, to be influenced.
For reasons already stated, embodiments of the supercharged internal combustion engine may further include in which the recirculation lines branch off from the exhaust-gas discharge system downstream of the turbine.
In this context, embodiments of the supercharged internal combustion engine may further include in which at least one exhaust-gas aftertreatment system is provided in the exhaust-gas discharge system between the turbine and the branching-off recirculation lines. Since exhaust gas is conducted through the compressor, the exhaust gas may be subjected to exhaust-gas aftertreatment downstream of the turbine.
Here, embodiments of the supercharged internal combustion engine are advantageous in which a particle filter is provided as exhaust-gas aftertreatment system for the aftertreatment of the exhaust gas.
To minimize the soot emissions, use is in this case made of a regenerative particle filter which filters the soot particles out of the exhaust gas and stores them, with said soot particles being burned off intermittently during the course of the regeneration of the filter. The regeneration temperatures of the particle filter are approximately 550° C. in the absence of catalytic assistance. Therefore, additional measures are generally implemented in order to ensure a regeneration of the filter under all operating conditions.
The regeneration of the filter introduces heat into the exhaust gas and increases the exhaust-gas temperature and thus the exhaust-gas enthalpy. A more energy-rich exhaust gas is thus available at the outlet of the filter, which exhaust gas can be utilized in the manner according to the disclosure.
Embodiments of the supercharged internal combustion engine may further include in which an oxidation catalytic converter is provided as exhaust-gas aftertreatment system for the aftertreatment of the exhaust gas.
Even without additional measures, oxidation of the unburned hydrocarbons and of carbon monoxide duly takes place in the exhaust-gas discharge system at a sufficiently high temperature level and in the presence of sufficiently large oxygen quantities. However, on account of the exhaust-gas temperature which falls quickly in the downstream direction, and the consequently rapidly decreasing rate of reaction, said reactions are quickly halted. Therefore, use is made of catalytic reactors which, using catalytic materials, ensure an oxidation even at low temperatures. If nitrogen oxides are additionally to be reduced, this may, in the case of the Otto-cycle engine, be achieved through the use of a three-way catalytic converter.
The oxidation is an exothermic reaction, wherein the heat that is released increases the temperature and thus the enthalpy of the exhaust gas. A more energy-rich exhaust gas is thus available at the outlet of the oxidation catalytic converter. In this respect, the provision of an oxidation catalytic converter may utilize of the exhaust-gas energy according to the disclosure.
Embodiments of the supercharged internal combustion engine may further include in which a bypass line for circumventing the cooler is provided, which bypass line bypasses the EGR cooler and by means of which bypass line the exhaust gas that is recirculated via the exhaust-gas recirculation arrangement can be introduced, circumventing the cooler, into the intake system.
It may be expedient to bypass the EGR cooling arrangement for example in order to prevent heat from additionally being introduced into the liquid-type cooling arrangement of the internal combustion engine. Such an approach is expedient if the liquid-type cooling arrangement of the internal combustion engine is already highly loaded, for example in full-load situations. If the exhaust-gas recirculation arrangement is utilized during the course of engine braking, it is likewise expedient for the hot exhaust gas to be recirculated without being cooled.
Embodiments of the supercharged internal combustion engine may further include in which a liquid-type cooling arrangement is provided for forming an engine cooling arrangement.
Here, embodiments of the supercharged internal combustion engine may further include in which the at least one cylinder head of the internal combustion engine is provided with at least one coolant jacket, which is integrated in the cylinder head, in order to form a liquid-type cooling arrangement.
A liquid-type cooling arrangement may decrease the thermal loading of supercharged engines more than that of conventional internal combustion engines. If the cylinder head has an integrated exhaust manifold, said cylinder head is thermally more highly loaded than a conventional cylinder head which is equipped with an external manifold. Increased demands may be placed on the cooling arrangement.
In this context, embodiments of the supercharged internal combustion engine may further include in which the liquid-type cooling arrangement has a cooling circuit which comprises the coolers of the exhaust-gas recirculation arrangement.
If the EGR coolers are incorporated into the cooling circuit of the engine cooling arrangement, numerous components and assemblies needed to form a circuit basically need to be provided only singularly, as these may be used both for the cooling circuit of the EGR cooler and also for that of the engine cooling arrangement, which leads to synergies and cost savings, but also entails a weight saving.
For example, only one pump for conveying the coolant, and one container for storing the coolant may be provided. The heat dissipated to the coolant from the internal combustion engine and from the EGR cooling arrangement can be extracted from the coolant in a common heat exchanger (e.g., a radiator different than the EGR cooling arrangement).
The exhaust-gas energy or exhaust-gas heat that is absorbed by the coolant in the EGR cooling arrangement can thus likewise be utilized more easily, for example for warming the internal combustion engine or the engine oil.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.